Strong far-away effects of local cloud seeding. Progress in technology depends on intense studies of these phenomena

~ FAR·AWAY EFFECI'S OF LOCAL CLll.JD SEEDING
Progress in Technology Depends on
Intense Studies of These Phenanena
Jerzy Neyman
Author Note: Jerzy Neyman is Professor Emeritus
Recalled to Active Duty and
Director of Statistical Laboratory
University of california
Berkeley. CA 94720
-1-
J. Neyman (2)
Public Law 94-490, enacted in October, 1976. directs the U.S. Secretary
of Conmerce to fonnulate an appropriate national policy on "..eather nxiification
While the lro'hole domain is vast, the thinking of the general public and of many
scholars focuses on the so-called cloud seeding as a means to enhance precipi-tation,
rain or snow.
In a recent article (1) I showed that, because of lack of randomization
because
or/of defects in its implementation. the claims of success on the part of
cloud seeding industry are not trusTh'Orthy. Also, the same article docwne~ts
that the many reports from apparently authoritative sources are slanted and
mreliable. (kJ. the positive side. the same article noted the phenomenon of
unexplectedly large apparent effects of local cloud seeding observed at
mexpectedly distant areas. This phenanenon. observed in two seven-year
long experiments conducted with marked effort at strict randomization. appears
as a most promising object of future studies.
The above.J
<:;;"eneral picture of precipitation augmentation technology is confirmed by the
recently published docunent (2) dated Jlale 3D, 1978. This document, ''The
Management of Weather Resources." addressed to the Secretary of Con1nercc. has
been fomulated by the Weather M:ldification Advisory Board chaired by Harlan
Cleveland. Interestingly, the Board recognized the necessity to create a
Statistical Task Force and there appeared a lack of unanimity. This is re­flected
in the Report of the Board being published in two vohmes. Volume II
represents the Report of the Statistical Task Force to the Board as a whole.
According to Harlan Cleveland (Vol. II. p. ii), ''The Board's own judgements
do not always follow the statistical findings to their ul timate inconclusive·
ness." The attitude of the Statistical Task Force is illustrated by the
following three quotations: (i) "randomization has come to he recognized
as an essential part of gathering trustworthy data about weather lOOdifica­tion."
(il) "randanitation... needed if we are to be able to usc the results
J. Ne)'lMJl (3)
as solid evidence." (iii) ''The details--and not just stmnaries--need to be
available... ". While ~ BJ!! in full agreement with all the three items quoted,
appreC1atlve
[ am especially / of item (iii) being published in the Report of
the Advisory Board.
The Statistical Task Force was conposed of three persons: David R.
lrillinger, Lyle V. Jones and John W. Tukey, Olairman. The analyses of this
:ask Force seem to have been limited to a few latest substantial experi­le1\
ts. The "strong far-<no'SY effects of local cloud seeding" ....-ere noticed in
of these experiments indicate
lxperiments performed earlier. The data / that "local" seeding of surrrner-
:ime elotds may have far-away effects that are stronger than those at the
;ite of seeding. In sc:ae cases, the seeding of clouds in a "target" A appears
:0 double the rainfall in a far·a....'Sy locality B. But in some other cases, the
e~ding at A appears to reduce the rain in B to one-half or even to one third
,f what would have falled without seeding. If these indications reflect real
,henanena, then the understanding of the underlyillli: atmospheric mechanism
'QuId constitute a very important contribution to the weather modificat ion
ecbnology.
The purpose of the present paper is to asselilble the evidence relatifl!
the far~away effects of local seeding of summer cumulus clouds and to
indicate 8 hypoU:etical mechaniSCI thereof. This lIlcchanl~m explain:!! SOll:f' of
~h~ elllp1rical Und1ngs, but not all. ]n ~articu1ar, the large far-ell.ay
J. Neyman (4)
increases in rainfall appar£ntly due to scedil'l<: that occl,;rred 1n certain
circumstances are not explain€d. Ilere, then, an appeal for cooperation of
interested atllospheric physicists 1s 1n order.
The plan of this paper is as [OU0101S. Hr:st, the lIuninp of the 50:11(:_
What vague terlls -Car-away efrects of local seeding" is clerifiec. "text,
evidence of far-a101ay effects of local 8udlng is presented, stemming from ~
t'olO experiments, eme in Switzerland and the other in Arizona,)
<;Th~~-f~l~\I~~~~~'hy-;U;eiliallIIE'chaniSll
that explains a substantial part or t'lIIplrical l"indin5s. Finally, cE'Tlaln
-findings of in-depth studies are pointed out that the proposed mechanism
fails to explain.
Figures 1 and 2 aTe intended to illustrate the iIleaning of the ter"llls
-local cloud ~eding- and -rar-a\o-ay effects- therecL Fig. 1 giVES a
schematic Illap of a region that includes substantial parts of Switzerland
and of Italy. The word Ticino marks the approximate location of the Swis~
canton bearing thi~ name. During the sum:lICrs of seven years, lS51-1963,
the tan ton Ticino the -target- of a randOlllized cloud seedif'll
experiment (3) Grossversuch III. The purpose of the experi.lllent was to ver-iCy
the hypothesis that the seeding of olouds with 31lver iodide (Agl)
smoke w111 suppress hail. However, rainfall was aho a subject of study.
In the present paper the discussion of Grossversuch III 1s Ha1ted to rain-fall.
The AgI SlIoke was dispersed frOlD a nUlllber cf generators lIIountEd on
tops of hills surrounding the intended target.
The seeding in T1cino exemplifies the lIIeaning of the terill "local"
cloud seeding. In order to illustrate the term -Car-away eCfects," F1j:. 1
exhibits seven shaded areas loc:ate.d around 1icino. 1\:0 01 t.hese ar(;as,
marked Zurich and Heuchatel, are 1n Switzerland. 1 atD indebted to Dr. Max
I t. MEDITERRANEAN SEA
Fig. 1. Area of Grossversuch TIl.
J. Neyrnn (4a)
J. Neyman (5)
Scmtepp of the Swhs Central ~eteoroloflical Office fer providing rain data
free: 20 raingages in each of these two areas. The reJCaining 5 ~haded areas
in fig. 1 are in northern Italy. Here, the nUlllber of ~ages per area varieo
CrOlD 1 to 15.
The -as the crow fliE'S- dhtsnces of the sev€.n shade<! areas in fig. 1
CrOlll the canton Tic1no are large. ~'or eX8:llple. the distance of the Zurich;
area is of the order of 120 kll. and that of the t.t1uchatel area of the q;rder
of 180 kIl. Both th€.se areas are separated frOIl Ticino by the i~pressive
bodie:l of the Alps. In the .a.lI.r.1..2l:i. unlikely event that the seeding of
clouds over Ticino affected the rainfall in any of thE' shaded areas in Fig.
1, such effects would be termed "far_away cffect3 01 local cloud setdinjl'".
As will be described below, very large apparent" far-away effects" of
local cloud seeding over Tic1no did actually occur. Depending upon atlllos-pher1c
conditions, :.uch as inversions and winds aloft, they were "positive"
or -negative". tk)wever, this happened in very special climatic and topo-graphic
conditions: in the vicinity of the ~dit€.rranean and near the
impressive Alps. The illlportant Question is whether any similar phtno.encn
is noticeable elsewhere. Here, Fig. 2 is relevant.
Figure 2 gives a scheJ:latic map of an area in Arizor.a. ncre, ever the
sUlIlIIler lI:onths of ~ven yean:; a rar.dOGtized cloud seeding experiment was
perforllle<! ( 4 ) by Louis J. f:atlan, Professor at the Univers1ty of
Arizona, Tucson. The €.Xperimcnt was cClIIpo!!ed of two parts labelfd "Pro-gram:!!".
PrograOl 1 exten(!ed over fovr years, 1957-1960, and PrO,;t:ram 2 over
three years, 1961, 1962 and 19611. The intention 01 tM experiment has to
verify ~he hypothesis that cloud seeding over the santa Catalina Mountains
could increase the rainfall. The second program differed from the first
principally in the following respect:.: (1) the target area in the ::.anta
J. Neyman (Sa)
J\ fSANTA
.,~ ~
~INA
MrS
~ooo
TUCSON Q
~400FT.) Q
~
o
G:l*iu}-{)
40MBSTONE
14500 FT.I
()
ARIZONA
MEXICO
Fig. 2. Area of the Arizona experiment.
J. Neyman (6)
Catalinas was some~·hllt smaller, (11) the r.urober ot e:ag£15 (all recording
gages) was increased, (iii) the dE'finition of a "suitable- day was somewhat
1II0re stringent, and Bv) the level above the ground at "llich the Agl smoke
was dispersed by a se«ler airplane Io'aS altered. basically, E;attan's
eVllluation of the experiment contains two parts, one each for the tlo'O 1'1'0-
grams. However, SOl:le questions were studied using all the available data'
combined. here, then, the seeding over the target in the santa Catalinas
(some 32 km. across) represents -local cloud seeding-.
In addition to this target, fig. 2 eXhibits a small Shaded area,
100 0. t.o the SSE fr<:1II the Santa Catalinas. This l!'hadcd area marks Walr!ut
GUlch, where the U.S. Department of Agriculture maintains a very dEnse net-work
of recording raingages, intended for the investigation of a variety of
phenomena such as soil erosion, etc. The person in charge of the Walnut
Gulch netl'Ork is Dr. Herbert B. Osborn. A cooperative study \oIith Osborn
(S, indicated that, on days "tlen Walnut Gulch val!! approximately "downwind",
the "local cloud seeding" over the Santa Catalinas was marked by vcry large
seed-no seed difference in rain in Walnut Gulch. If -real", that h, if
not caused by vagaries of randoehation, then the tel"lll -far-avay effect or
local cloud sel!'ding-/~W~ to this phenomenon.
Our studies of far_away effeClts of local seeding were motivated by the
question about the validity of the cross-over exper1Jllental design. As
deacribed by E.J. Smith (6), the cross_over aesi(!n originated in Australia.
In thi15 design there are two "targets," say T, and T2 , not very distant, so
that the time periods (perhaps days) that are judged "suitable" for clOUd
seeding in one of thell arE: also suitable for seeding in the other. Then,
experilllental cloud seeding is perfo)"lllled on all clays that are jUdgEd ~uit-able
in the general locality containing 1', and 1'2' "hen such a day
J, Neyman (7)
arrives, a randomized decision is made as to whether to see<! il'l 1, or f
2
,
This procedure doubles the number of observations possible during a liven
experi~ental season, which is a considerable galn, In addition, the theory
deVeloped by P.A.P. !".oran (6) indicate" a very advantageous possibility of
using the non-seeded target as a control area for the other target.
Obviously, if no far.away effect!! of local seeding exist, then the
cross-over design is very attractive, which explains its frequent use. I:.ut
,,"hat if seeding over 1 1 produces a substantial effect on precipitation in
T
2
, and vice versa?
Prior to de"cribing our efforts to study the far-away effects of seed-ing
at (irossversuch III, it 1s necesu.ry to Illention briefly an earlier
finding. llIls 1.:'1 that the effects of seed ins on ratn in 11cino itself
depended on the pre~e[lce or ab~ence of stability layers (inversions or
thick lsothermals) as revealed by the noon radiosonde at Milan (7). It
appeared that·, in the presence of stability layers the apparent effect of
seeding on rainfall in Ticino itself was a large and !!ignit1cant increase
in rain. On the other hand, on day" with uninhibited updrafts, the
apparent effect of lleeding wall also large, but negative and not Quite siF,-
niCicant by CU!lt01ll2ry standards. Eecause the et!ectiveness of silver
iodide as a nucleating agent of ice crystah 1.:'1 l1eited to supereoole<\
clo~", with temperaturell below _50C, both findings appeared unexpected .
. Ho~ver, independent studiell or Ne1burger and Chin at V.C.L ..... (7) and of
M. Sch\1epp and J.C. Tha!lls of Zurich (unpublished) provided a convincing
explanation of the enhancement of rain by seeding under stability layers.
On the other hand, the absence of large increaus in rain on days with
uninhibited updrafts appeared lIlyllterious. As a conllequencE of these find-ings,
the later effort to see whether the local ec,edint in Heino was
J. Neyman (8)
accompanied by the far-away effect~ in the sha::led areas of Ht,. " was eon-duoted
\11th a stratirtoation: separately for days \lith uninr.lbttfOd
updrafts and separately for days with stability layers,
~.Qf Ia1:-Al:!n Effects £! Seeding
jo~lll
The results of cur first effort to etudy the possibill ty of far-a'lo'ay
effeot.!! of seeding over Hoino are exhibited in Table' reproduoed from
(8).
It 1.5 Men that, in the presence of stability layer5, the 100al seed-ing
in Heino wa5 aocompanied by exee55es of rain in all the 8 localities
studied, that in 6 or thel!le loealitiee the apparent inoreases in rain "ere
(two-tail P)
greater than 401 and that in 3 of them they werE' significant/at better than
Sf;, Or! the other hand, on days with uninhibited updrafts the apparent
effects in 6 areas wre nfOgative, but none Of them significant by customary
:!tandards.
Confronted by the re.sults for day.s \11th stability layers, particularly
",ith signirtcant apparent gains of more than SOl in rain near Zurich and
Neuehitel, Dr. SCr.J'epp \la$ incredulous and =:ade tl.'O sugge.sUons. According
to ScbJepp, the prinoipal source of mol$ture in the atmosphere over
S\oiitzerland Is the licditerranean, in the south. ThUS, if one stratiflf's
the Grossversuoh 111 experimental days aocording to 'Io'ind direotions loll th
velocity oomponents frOlll the south VS. those from the north, the stUdy of
rainfall data in the eight areS$ lIIisht oontribute to the hypothesi.! of
oausality with seeding in Ticino. SCl'iJepp's other sU,gll;eetton lOas to Invcs-tigate
the t1llling of the apparent effects of seeding in the various ar('a:s,
Table 1
,I. Neyman lMaJ
Effects of Clron1'ersuch III seeding in Ticino on rainf&11
in millimeters, fallen in 8 areu, averaged per experimental day.
Days with uninhibited updrafts DaylJ with stability layers
47 seede<l, 50 not seeded 96 seeded, 94 not seeded
An. NS ~ '5 ~
change change
ZUrich '.5\ 7.0_ -35 0.11 6.98 1t.19 lfeuchitel 4.43 +61 0.012 5.86 -2' 0.32 6.811 1,.36 +'" 0.031 'I'ic1no 1.98 12."5 -36 0.15 11;.418.82 +61 0.031 Brescia 4.18 6.6' -31. 0.079 6.09 1t.17 +.6 0.066 Turin 4.24 4.01 + • 0.90 5.615.41 + • 0.89 Milan 2.93 3.78 -22 0,113 5.683.90 +" 0.13 Fidenza 3.76 3.94 - , 0.87 5.263.68 +13 0.15 Genova 3.13 3.20 +16 0.65 4.243.65 +16 0.60
Table 2
erects of seeding 1n Ticino on the rainfall In 8 areas on days with and without
stability layers, vHh loy southerly and northerly winds
= J:ean precipitation on seeded days, !IS on not seeded, p. significance probability
Days yith uninhibited updrafts Den with stabilitv lavers
Oars with lov southerly winds
25 seeded, 22 not seeded 48 seeded, 116 not seeded
NS % '5 ~
effect effect
ZUrich 5.22 1.20 -21 0.39 8.81 4.01 +11 0.00
Hcuchatel 5.51 7.22 ->' 0.46 8.118 5.16 + 6' 0.060
'I'icino 12.40 19.21 -35 0.23 17.78 8.61 +106 0.018
Brescia 5.38 9·85 I, 0.11 6.30 11.75 +33 0.33
Tufin 5.65 '.81 +16 0.13 6.29 3.21 + 93 0.063
Milan 3.96 ,.60 -29 0.1I1t 4.61 3.116 + 35 O.l~2
F1dem:a 3.43 6.01 -13 0.23 3.114 3.15 + 9 0.81
Gen01'll 3.96 3.91 + 1 0.98 2.16 3.00 - 6 0.84
Oars with low northerly winds
19 seeded, 25 not seeded 112 seeded, 37 not seeded
'ZUrich 11.32 6.90 -31 0·29 ,.)8 11.05 + 33 0.1.1
Neuchitel 3.55 11.19 -15 0.11 5."8 3.54 + 55 0.21
'I'icino 3.28 1.60 -32 0.42 11.03 8.16 + 26 0.56
Brescia 3.14 3.11 -15 0.62 6.22 3.12 + 61 0.11
Turin 2.98 3.21 - 9 0.86 5.02 9.18 -" 0.15
MHaa 1.95 2.46 -21 0.60 1.26 5.01 +" 0.31
Fiden:r.a 1;.113 2.41 +19 0.11 1.92 5·11 • 55 0.23
Genova 3.60 2.60 +36 0·51 6.31 5.28 • 1. 0.66
J. Ne"..., (9)
Table 2 reproduced frolll (8) and Fig. 3 give thE' results of these :!:tu<lies.
The wind directions used to Froduce the rezult.s in Table 2 are tho~(;
pUbllsh"d in the annual reports on Grossversuch Ill. They are based on the
noon radiosonde at Milan at the IIltitude of 1,500 meters above sea level.
In interpreting Table 2 onE' must bear in llIind l'-'O olrcUIlISlancel:l. One is
that the terms ·southerly· and "northerly· windS are sUbJl!ct to lnterpreta- ,
tion. "partiC!ular day in the "southerly" category could have a wind ¥ltt.
a strong easterly velocity component .nd only a very weak cOllIponent from
the south, etc. Another importtnt circUlIIstance is that /Dany of the
raingagas used 1OE'l"C located in deep canyons with varying directions. 1'h!
combination of these two factors must have contributed to the many irreyu-larit1es
1n the general pattern or Table 2.
However, the stability layer$ part of Table 2 does reveal a contrast
between the apparent seeding effects on southerly and northerly lo'ind days.
In particular, the apparent increases in rain in Ticino and near Zi!rich
with southerly winds exceedeel 100J anel their significance probabilities
became impressive. This is in contrast with the part of Table 2 for days
with stability layers and northerly winds. The general impression ravorine
causality between seeding and the indicated pettern of rain in far-away
localities is increased by Fig. 3.
fig. 3 refers to days liith stability layers. It is based on hourly
precipitation data kindly provided by Dr. 5ehuepp. fig. 3 has t'-'O panch,
one for southerly and the other for northerly winds, and each panel €xhi-bits
tioiO curves, one for days seeded in Ticino and the other for controlS.
The vertical lines lIlark the scheduled period of seeding in l1eino, lb hours
beginning at 7:30 a .....
SOUTHERLY WINDS
J. Neyman (9a)
3 HR. MOVING AVGS
--SEEDED
------ NOT SEEDED
NORTHERLY WINDS
75
60
45
15
OJ-+~~:-:-~+::-~----"
GAM 2PM IOPM 6AM 6A
HOUR
38 S
46 NS
..... SEEDING PERIOD~
2PM 10PM-,--·GAM
HOUR
Fig. 3. Diurnal var.iation in hourI)' rainfall in Zurich when
it was approximately downwind and when it was approximate!)'
upwind from Tieino.
J. Neyman (10)
It is seen that the average hourly rainfall in Ulrich on seeded days
with southerly winds began to lIIarkedly exceed that on days without seedint
sollie time in the afternoon, S to 1 hours after the ~cheduled commencement
of seeding. This difference continued for quite a few hours. flo such
striking effect appears noticeable on days with northe:-ly "'inds.
U; lI:entioned at the outset, the second source of evidence or far-alo'ay
effects of seeding sUllllIJer clOUds is the Arizona experiment. Here, the con­ditions
were very different frOIl those in Groseversuch Ill. In addition to
olimate and topography. there liere important differences in experill!ental
de~is:t1: method of seeding and randomization. \lihereas in Gros"versuch III
the A,gI smOke wa" disper:'led from the ground over 1~ hrs., Croll 1:30 a.m .•
in the Arizona exper1.lllent this liaS done frOlll an aircraft over 2-il hrs.,
beginning at 12:30 p.m. The level of seeding above the ground i" likely to
have been above warlll stability layers, if any were present. Also, while
the Grossversuch.practice approximated a 50:50 unrestricted randoaization.
the de"ign in Arizona ...as in not completely randomized pairs of "suitable­days,
subject to the restriction that the two days of a pair be separated
by not more than one day diagnosed as -not suitable-. t·or the first day or
each pair, the decision whether to seed or not lo'aS purely random. khatever
this decision wa.s, it required a contrary decision for the .second day. If
the first day or a prospective pair 10ias ColloWE'd by two non-suitablE' days,
then this f1ret day of thE' incipient pair was discarded and thp continua­tion
of the experiment awaited the arrival of another day diagnoecd "suit­able."
that could becolliE' the first day of an incipiE'nt "air, E'tc. In
J. Neyman (11)
consequence, the ,!;econd days of all the experimental pairs, 106 or them,
are marked by the fact that their 5u1tabllity was diagno~('d with full
knowledge whether they would be seede<l or not. Thh circumstance reouire::
that evaluations, whether of the entire expcr1.Jlent or of a ::tratUII,be in a
"triple": (1) all days, (11) first dayt' of pairs and (111) ::cccnd
days.
Table 3, part of the table publi~hed in (9), p:ives the apparent
effects of Santa Catalina ~unta1ns seeding on the noon to noon 211 hI'S.
ra1nfall 1n Walnut Gulch, average<l for exper1mental day, ...·hether wet or
dry. These results for "alnut Gulch are compared with similar data for the
211 hI'S. precipitation in the Santa Catalina target itself. :;ymOOl f'
denotes the t'lro-tail significance probability.
Symbol N'Ji marks days with ncrthwesterly winds on which "alnut Gulch
waa approximately downwind from the site of seedin£:. Symbol S£ standS lor
days With southeasterly winds, that 1s, all experimental days other than
those marked IiW. The directions of winds are those of the level of seed ins
as recorded by the 5 P:III. radiosonde at Tucson.
It is seen that, while all the apparent effects in table 3 are nej!a-the,
the two stratif1cation15 of daY15, namely tila' (when Walnut Gulch ....a~
approxiDlately down....ind) vs. Sf days and the 15tratif1cation of 1st days vs.
2nd. days, exhibit ir.terestin,g contrasts. On ~loi days, thE" apparent loss of
rain in the Santa Cabl1nss is negligible, but at \.'alnut Gulch it 1s vcry
large and highly s1gnificant. This 1s contrasted on SE days: a s1gnlfi-cant
1101 loss of ra1n 1n the Santa Cata11r.as V8. a moderate and a non-significant
1058 1n Io'alnut Gulch. The contrast for the second strat1f1ca-tion
is less striking but it i5 1n the same p.eneral direction: the stratVlll
which is less favorable in one of the two 10ca11 ties is more favorabl~ in
J. Ne)'lla1l (l1a)
Table 3. Apparent effects of cloud seeding over Santa Catalina MountaIns
on 24-hour precipitation in target and In Walnut Gulch, Adzona.
(Both Prograllls are included.)
Rainfall over Rainfall over
Santa Catalina Walnut Gulch
Category Inches %S Inches %.!:._._~
, All days
S 0.125 -30 0.06 0.093 -40 0.02
NS 0.179 0.155
N\I wind
S 0.120 - 9 0.78 0.039 -73 0.01
NS 0.133 0.142
SE wind
S 0.127 -'0 0.03 0.115 -31 0.17
NS 0.211 0.166
1st days
S 0.126 -)4 0.13 0.115 -14 0.63
NS 0.189 0.134
2nd days
S 0.125 -35 0.31 0.075 -58 0.01
NS 0.166 0.181
J. Neyman (12)
the other.
The resul ts for all experimental days of the Arbona experiment 1n01-
cale a 301 apparent loss of rain 1n the target, significant at 670 and a 40J
apparent far-away 10311, significant at 2".
Figure II, reprocluced trOll! (1 ), indicates that the striking seed day
rain def1ciencles when \ialnut Gulch was approximately downwind from the
seeding site began to be impressive at about 5 or 6 p.lll. and lasted poI:lt
1Il1dnight.
The above results, suggestive or the far-away· eCreeLs as they are,
have been obtained by a lIolllewhat crude method. In order to study tht'l
downwind effects, the experilllental days /28;1~~ ~:~~OS:deG~:~:~erllUCh ill
and 210 1n Arl:tOna --------------3I>had to be
split into two parts, o~e with the areas of interest belnp: approximately
downwind and the other wab tbeu area5 being upWind. Any further stratif-ication5
requirE'd the analysis to be lIlade on a relatively small numbE:r or
observations, wi th the consequent decreal!!e In preci"ion. A so~ewhat lI:ore
in-depth lIIethodology, provides t.hE' pos5ibillty of studyin~ the wind direc­tion
influences usin@' all the available expnimental data simultaneously.
rhis lIlethodology, labeled "lIloving grid" or "mogrld" lIlethcdology, was
1eveloped (10) us1ng the idea of R.R. Braham who developed it fOT radar
lata.
The study of thE: AriZona uperillc.nt u"ing thE: lllOgr1ds (11) ends With
.he following ~ketch of a hypothE:tical lIIechani.:llll (P.H, for short) of the
J. Neyman (lZa)
3 HR. MOVING AvGS.
--SEEDED
------ NOT SEEDED
765
64 NS
S E WINOS
JO 15 20253035
HOUR
N W WINOS
025 295
f 8. 41 NS
~
020 0:
l!'
z .015 '" f\
0 z ! \v\
~ .010 § ~ \
0: "'i \
~ ,
0
,
Q.
JO is 20 25 30
tnJR
Fig. 4. Diurnal variation in hourly rainfall in Walnut Q.llch
when it was approximately downwind and when it was approximately
upwind from santa Catalina I>btmtains.
J. Neyman (13)
far-a1ol8Y lOiSsez ot rain:
·1he seecing 1118Y have initiated rain high above the Fround; ""hen
falling through dry a1r, this rain ev~porated and oecreased thE'
temperature; while carried downwind, the parcel of cool air evcn-tually
reached the ground and inhibited convection."
The relevance of the evaporation of rain before it reaches the l!l"ound
seell5 to bavl' been ftrst noticed in 1962 by LJ. korkman. 1 reyret
that I overlooked his publication for a 10nl: tll1le. Subsequent studios arc
due to Schiiepp, J. Joss and H.P. Roesli (12).
\Ie now proceed to assemble empirical evidence favoring the above
hn.,thetical mechanism. Indications are that this ll:ccr.anlSll opt'ralcd not
only during the Arizona experiment, but aho on tDe uninhibited updraft
day-, of Grossver:!'uch Ill. t:o~ver, some of the evidence indicates a
phenOlllenon not implied by the hi'l: large increases in rainfall cccurring in
certain conditions. The atmo~pheric-physlcal aspect of the.se conditions
appears as a very important problem.
J. A.S.
Figure 5, redrawn from a figure publl::lhed by/Slmpson and !Dennis (131,
illustrates the happenings to a SUIIllller cw:lulu.s cloUd SUbjected to :seediny'.
The legend states thtlt the figure represt!nts photoJl;raphs Ulustratiny thr
"cut-off tower rep-illle which often follows dynamic seedinp; of a dn;rle
cumulus." It/ah reference to tiM, Hg, 5 illustrates the fact that the rain
ln1tiated by seeding can e.stablbh a ·cut-off tOlOer rep:ilr.l',· pre:su:aably by
ccoling the lower part of the cloud. The tenD used by the two authors is
"precipitation break,· This, however, does not documEnt tinything tlbout the
Arizona experiment. Certain happenil\l~ at the Arizona cxperilllcnt are
lliustrated by fig. 6. This figure illu.strate.s the patterns of winds aloft
'ecorded by the 5 p.lI. raclio,sonde at Tuc!'on. Ihe:::e observations ellist for
J. Neyman (13a)
PANEL A: Cumulus at time of seeding.
PANEL B: Same cumulus 10 minutes after seeding.
PA~EL C: Same cloud, split into two parts.
18 minutes later.
Fig. 5. "Cut-off tmier regime which often fo11O\o1's dynamic
seeding of a single CUlIJlus."
J. Neyman (14)
210 experimental day~ of the Arizona experiment for wtlich the radiosonde
data are available. f'iS. 6 !tives an 1llu.!trative sample of the data. ~ach
vector of a seQuence give'" tht dirtction of the wind at a tpec1fied level
above the ground, llIeasured in 1II1l11bar~, frOlll 900 a:b. to 200 lIIb. Alse th"
length of the vector !tlve:! the lIind vf'loci ty. A closer inspt"ction of f ip.
6 ind icatcs two contra.sting type.s for ""hich the ~'Ork('rs at berkel£y Sta-tistieal
Laboratory invented th" descriptive terlls "pret:r;els" and "lont
fellows."
The term "pretzel" refers to thE: regia:fI' of practically no lIind:! aloft
that prevailed during the rdatively brief peried of the asc"nt of the
radiosonde. ObViously, on days lIith sclKling over the Santa CatnJinae
lIIarked by the pretnl winds occurring during the 2_t1 hours of seeding
operations, the "precipitation break" phf'nOl:lenon can be reflected only in
the target itself. en the other hand, on days \Oith "long fello~'" wina:! at
an ap~ropr1ate level occurring during seeding, the ·preci~itation break"
llu.!St be carrieo away. possibly to lIIanifest itself in solte other locality.
The importal'lt question is whether any such f"ffects arc reflecteo in
actual precipitation dat.a. Thf" relevant findings of Proff"5sor Batten arE'
published in twe papE>r.e1
4
)In his 1967 paper Battan ,hows that on days wit.h
seeding over the Santa Catalina Nountain.e, there were relatively !tore radar
echoes in the clol)(ls than on day.e without :seedint, and that. this diner­.
ence, indicating the initiation of rain, was concentrat~d on cloUO:: \;1th
top temperatures between -2t1°C and _30°C, very cold. 1t eeC1ll5 likel)' that.
these cloud.e had their bases high over the ground. In the oth£r paper,
publbhed a year earl1f'r, Eattan .etudied the prf"cipitation reaching the
ground in his target from' p.m. to 6 p.m., particularly with reference to
the indirectly ceasured height of the clOUd ba~e.
\' J Neyman (143) j'"mcow ~
570708 Dole' 570709
l 1
570729 570730
Y ~
PRETZEL
570820
580724
LONG
570821
580725
Fig. 6. A saJJt)le of wind patterns aloft at 5 p.lII. of experimental
days durilllt the Arizona Trilil.
J. Neyman (15)
Panels 1 and II of Table II give data taken frOlll Battan'S Tab~.!l 7 and
8 referring to Programs 1 and 2, rC.!lyectivdy. The three lines of cact:
table refEr to days with cloud basc.!! "low," "lIIedium," and "high" as
indirectly meai!!ured by the so-called "dew-point spread."
lhe six categories of experimental days ",.ith low, medlu:ll and hiF"h
cloUd bases during the two Programs of the experiment are unambiguous in
showing seed day deficiencies of rain in the target. Solnewhat contrary
the conclusion of Eattan, this fact could hardly be ascribed to chance. lr.
the absence of effects of seeding ar.d given strict randomization, the pro­bability
of the Observed results is (1/2)6 ~ 0.016, ",hich is a respectable
one tail significance probability.
Pand III of Table" represents a combination of i'anel:! 1 and II.
HerE: the estimated percent effect given in the last column is unambiguous:
the higher the cloud base, the larger the lo:u of rain ascribablE' to S('o-ing.
This result suegests that during Battan's seeding in the early aftcr-noons
the appropriate lev£! winds over the Santa Catalinas iIIust have been
In conSl.quence, the 5-hour precipitation alllounts, I p.m. to b p.Ill.,
on ....hich hattan's Tables 7 and 8 are based, reflect the full ,,;('iFllt 01 tl'.E'
"precipitation break" phenomenon recorded by ::'illp~on and Dcnnis.
This concludes the arguments suyportinl': the hypothetical mechanism of
(ar~a\;ay effects of local cloud seeding. This mechani:!Cll is bau(! on the'
• Simpson_Dennis phenOll!enon of -prt'cipitation break.- ...o ....e\·er, in addition
tc this phenomenon the h,.o authors mention anothcrf;;::ce:ctn~n;
labeled "orphan anvil".
-In both tropic~ and temperate latItude::: 'orphan anvils' frolll
I'latvral cumulo-nilllbus clouds arc foul'ld several hundred mile:!! and
lIIany hovre frOlll their ai te of origin. figur(' 29 .:lhc\o:s an
J. Ne)'1llan <lSa)
TABLE 4
Dependence of the apparent effects of seeding at the Ari20na expet"i_nt
on the indirectly .-easllred height of the cloud base, rain from 1 plll. to 6 pm.
PANEL 1. Data for Program 1
Seeded days Not seeded days Percent effect
Cloud base No. Mean rain No. Hean raln 100 (S-NS)/NS
"low" 25 0.071 28 0.078 - ,
"medilJlD." 20 0.036 18 0.062 -42
"high" 2J 0.013 22 0.034 -62
PANEL 11. Data for Program 11
"low"
"medium"
"bigh"
17
I'
0.086
0.035
0.028
10
I'
0.144
0.067
0.041
·'0
·'8
-32
PANEL III. Height of cloud base and the apparent effect of seeding
at the At"iz:ona expet"iment. Data for both progralaS combined.
"low"
"medilllll"
"high"
42
"29
0.077
0.036
0.016
38
37
30
0.095
0.065
0.036
-I'
-"
-55
J. Neymn (16)
extensive anvil streaming out frolll an eXj:;loding st'f'dcd cumulus in
Florida, a not unCOI:lIIOn event .. In addition to their nucleating
potential, 'orphan anvils' could have important radiatiY(
iClpactS. Where ::olar racHation strikinl the j!.rol,lnd dir€'ctly
maintains convection, a:: over Florida in SUll1IIlcr, the shade of a
single anvil often \o:ip.E's out cuI:/lul1 over a sizeable fraction of
the southern peninsula extending out~ard in any direction from
the target area, depending en wines aloft.-
The photograph of an orphan anvil 1'n f'igure 29 of the tIo'O authors
lOOks quite convincing and it is obvious that this phencG:enon can be ba~ic
in a lllechanislQ of the far_away effects of local cloud seeding. The problem
h tel secure data of a reasonably randOl:1zed exp<rillent including high
level winds, orphan anvils and rainfall in far-a..,ay localities.
As already mentioned, the methodology used in documenting far-away
effecls of lecal seedin!!: both at Crossversuch ]11 and in the Arizona exper-ill:
ent is quite crude. The difference bet..,een wind dtrect1on~ on two days,
say Dland. DZ' may be minute and yet a far-away locality, such as Zurich or
.\laln~t Culch, lllay be considered "downwind:n~n day D1 and "upwind" on IlZ'
The lDogrtd ~cthodolO!y (10) perm1t!/to study the -do"''lI\o:indedness- or
"upwindedness", etc., of far-away effects defined with a lIluch rreate·r 111''''-
cision. Howevf'r, this advantage must be paid for. The price is that the
results do not apply to any specified locality at a known dietanct' from the
localities
site 01" tet'ding. They apply to catei-orie~ of / lOhlch on particular
days of an uperiment are within a $I':ccified range 01 di$tances from the
J. Neyman (17)
site of seeding and within a specified range of angles from the day's wind
direction.
Three panels of Figure 7 exeq>l ify the roogrid methodology in studying
the far-away effects in GTossversuch III (two panels on top) and in the
Arizona experiment (the lowest panel). There are 2 ranges of distances:
from 0 to about 140 kin. and from 140 kin. to about 280 kin. These are can-bined
with 4 ranges of the angle of winds: _45 0 to +450 from the day's wind
direction at a specified level ("downwind"), from 450 to 1350 ("to the right,"
etc.). In consequence, each panel of Fig. 7 provides room for evaluation
results in eight "cells". These cells are described as "far (or near)
downwind," as "far (or near) to the right," etc.
The lMgrids for Grossversuch III are based solely on raingage data from
the six shaded areas in Fig. I otber than ~1ilan. For this reason there are
no evaluation results for the four "near" cells.
The four numerical entires in particular cells are written in two lines.
Each top line gives mean rainfall on days with seeding and that on days without
seeding. The lower line &ives the estimated percent eff~ct, which can he
positive or negative. The second entry is the two-tail siWlificance probabi­lity.
Cases of significance are marked by underlining.
As an illustrative example, consider the top panel of Fig. 7. It corres­ponds
to Grossversuch III days with uninhibited updrafts, for which Table 2
exhibits a substantial prevalence of negative apparent effects of seedin(i:, both
with southerly and with northerly winds" none of them significant. Contrary to
this, the far-dowm,dnd cell sho\;'S a highly significant 61\ deficiency of seed d­rain
ascribable to seeding. How come? There are two reasons for this contrast
ll"le is that the evaluations in Table 2 are based on only 47 days with southerly
Ioinds and on 44 days with northerly winds, too few to achieve a substantial
power of the tests used. The other reason for the inconclusiveness of Table 2
may Io'ell be the crudeness of detenninin~ the degree of "dOW!l'l'.'indedness": the
Fig. 7
MOVING GRID RESULTS FOR
GRDSSVERSUCH III
AND fOR ARIZONA F.XPERIMEN1S
GROSSVERSUCH III
UNINH1BlT(O UPDRAFTS
GROSSVERSUCH III
STA81L1TY LAYERS
ARIZONA EXPERIMENTS
flRSTOAYS
J. Neyman (173)
./. Neyman (lSI
errors may have been in excess of 100°! Contrary to this, the mogrid methodo­logy
uses the towl 47 + 44 .. 91 days. Also, the error in deten'lining "down-windcdness,"
etc. had to be less than 45° either way. "ihile not too ~ressh
for sUTVeyors, this degree of precision appears encouraging for large scale
atJoospheric IOOtions.
The three panels of figure 7 exhibit indications of two intere~titlf
atmospheric phenotllena. One is the analoFY bch-een days ~ith uninhlbi~('O
updrafts at Grossversuch III and the Arizona experiment: in both cases the
far dOWl'llo'ind cdl is ~ar],ced by a larp:e and significant apparent 10i!S of
rain ascribable to ~eeding. Another 1nterestinp; detail 1s the pre~ence of
large and significant rainfall increases 11'1 the far cells to the right oj
the days' ..,ind direction for days with stability layers 11'1 Grossversuch III
and also for Ari2.ona.
The question is what could be th(' mechanism of these d1ffer('nccs in
rainfall on seeded and not seeded days? Thi~ question is of particular
where
1r::terest for Arizona I i111 otter evaluations indicated los::::cs or rain
ascribable to seeding. As is well ],cnolffl to meteorologists, there arc t\;O
distinct classes of SUDllDer convective clcuds: the "air lIless" and the
-frontaP eloeds. Could it be thet seeding of one of tr.('i!e categories
seeding of the other
decreases rain 11'1 the far down"'ind areas and that / increases rain in the
far areas to the right of the day's wind direction? And again: What is the
lI'IeChanism of this phenanenon?
J _ Neyman (19)
(i) "randomization has corne to be recognized as an essential part of
gathering trustworthy data about weather lOOdification", (li) "randomization ..
needed if we are to be able to use the resu1ts as solid evidence", (iii) 'The
details--not just slmllaries--need to be available... ". [Ref (2) of present
article.] While being in full agreement with all three statements, I feel that
statement (iii) requires illustrations.
Roughly, there are b.Q types of regrettable omissions. lXle is the anis-sion
of details of the experiments performed, of original data and of methodology
used for the evaluation. Not infrequently these details arc hard to get. A
somewhat different type of omission is illustrated by an article in the volume
Legal and SCientific Uncertainties of Weather Modification (Ed. W.A. Thanas,
Me University Press, 1977). The article in question is a",thored by L.J.
Battan. Its title is ''The Scientific Uncertainties: A Scientist Responds."
en p. 28 we read: "1 hasten to point out that data from a number of carefully
done c.oomercial seedings strongly suggest that the person who paid for the opera­tion
got a fair return on the investment." This remark, representing the opinion
of Professor Battan, is an interesting "detail". However, I miss another detail.
Ibis is that Professor Battan perfonned a cloud seeding experiment lasting seven
5l.D'11l"1ers, that his own evaluation for the first four-year long "Program" indicated
lO~ l,ess rain on days with seeding than on those without, and that his own
~altiation of the second "Program" of three smners also indicated a 30\ deficien­;
y of rain on days with seeding. !-Iy feeling is that this missing detail of
>rofessor Battan's S-page It •••A SCientist Fbspond·5" is rather relevant for a
;onference "en Legal and Scientific Uncertainties ... " Also, it seems important
:or the government and for the public at large.
Regretfully, a tendency to accept reports without insisting on "details"
.s reflected in Vol. I of Harlan Cleveland's Report to the U.S. Secretary of
:ootnerce. I't'hile one year of intense study may seem long, it is not sufficient
J. Neyman (1
for gathering all the important details and for their appraisal. As stated i"
my article (1). the fonnulation of a realistic national policy on weather rrod
fication requires the "Establishment of at least two philosophically differen
interdisciplinary research groltlS, inc1u:l.ing statisticians versed in experi­mental
~rk, perhaps members of the National Academy of Sciences, with a spec
mission to reevaluate the data of as many already perfonred cloud seeding expc
mcnts as possible, ~ continuation of properly planned experimentation.; The
suggested research groups should have unlimi ted access to the same data and hI
facilities for personal meetings to exchange ideas. They should be funded fn:
sources other than those engaged in funding cloud seeding." To be effective
this IIIJ1tigroup project should last not just one but at least three years. He:
fully, such a nultigroup project would examine the indications of the impressi
far~away effects of local cloud seeding, including the studies made in the
Berkeley Statistical Laboratory. Even with the greatest care blunders arc
difficult to avoid.
J. Neyll'lan (20)
REFERENCI:S AND NOTES
1. J. NeYllan, Proc. Nat. Acad. Sci. 74, 47H-4721 (1977).
2. H. Cleveland, (Chm.) Weather Modification Advisory Board,
The Manageraent of Weather Resources (U.S. Gov't Printing
Office, Washington, DC, 1978) Vols. I and II.
3. Grossversuch III ;tur Bekampfung des Hagel 1m Tessin. Seven
annual reports dated 1958·1964, available from Centrale Meteor-ologica
Svizzera, Osservatorio Ticinese, Locarno-Monti,
Swi tzerland.
4. L.J. Battan, J. App!. f>leteor. 5, 669-683 (1966); L.J. Sattan,
~6,317-322 (1967).
5. J. Neyman and II.B. Osborn, Proc. Nat. Acad. Sci. 68, 649-652
(1971) •
6. E.J. Smith, in Proc. Fifth Berkeley Symposium on Mathematical
Statistics and Probability, L. Lecalll and J. Neyman, Eds.
(University of California Press, Berkeley, 1967), 5, pp. 161­176;
P.A.P. Moran, Australian J. of Stat. I, 47-52 (1959).
7. J. Neyman, E.L. Scott and f>l.A. Wells, Proc. Nat. Acad. Sci.
60, 416-423 (1968); M. Neiburger and H.C. Chin, ~ 60,
424-431 (1968).
8. J. Neyman, et. aI, Rev. Intern. Stat. Inst. 37, 119-148
(1969) .
9. J. Neyman, et. aI, Proc. Nat. Acad. Sci. 69, 1348·1352
(1972) .
If). J. Neyman, et. aI, Proc. Nat. Acad. Sci. 68, 147-151 (1971);
R.R. Braham, Project Whitetop--Report to the National Science
Foundation (Dept. Geophys. Sci., Univ. Chicago, 1965).
J. Neyman l2l)
11. J. Neyman, et. aI, Proc. Nat. Acad. Sci. 10, 351~360
(1913) •
12. E.J. WorKman. Science 138. 401-412 (1962); M. Schuepp. J.
Joss and H.P. Roesli, J. Appl. Meteor. U. 183-781 (1964).
U. J. Simpson and A.S. Dennis, NOAA Technical Memorandum, ERL
OD-14 (Dept. of Commerce, Boulder, CO. 1912). pp. 1-148.
14. I thank Shyrl Dawkins. Kathie Hall, I>larilyn Hill, Jeanne.
Lovasich and M. Tere Sanabria for their concerted effort in
assembling the widely dispersed evidence and for the
general spirit of cooperation. This article was prepared
with partial support of the Office of Naval Research
(ONR N000147SC0159) and of the U.S. Army Research Office
(DA AG 2916G0161). This support is gratefUlly acknowledged.
All the opinions expressed in this article are those of the
author.

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~ FAR·AWAY EFFECI'S OF LOCAL CLll.JD SEEDING
Progress in Technology Depends on
Intense Studies of These Phenanena
Jerzy Neyman
Author Note: Jerzy Neyman is Professor Emeritus
Recalled to Active Duty and
Director of Statistical Laboratory
University of california
Berkeley. CA 94720
-1-
J. Neyman (2)
Public Law 94-490, enacted in October, 1976. directs the U.S. Secretary
of Conmerce to fonnulate an appropriate national policy on "..eather nxiification
While the lro'hole domain is vast, the thinking of the general public and of many
scholars focuses on the so-called cloud seeding as a means to enhance precipi-tation,
rain or snow.
In a recent article (1) I showed that, because of lack of randomization
because
or/of defects in its implementation. the claims of success on the part of
cloud seeding industry are not trusTh'Orthy. Also, the same article docwne~ts
that the many reports from apparently authoritative sources are slanted and
mreliable. (kJ. the positive side. the same article noted the phenomenon of
unexplectedly large apparent effects of local cloud seeding observed at
mexpectedly distant areas. This phenanenon. observed in two seven-year
long experiments conducted with marked effort at strict randomization. appears
as a most promising object of future studies.
The above.J
' 0.46 8.118 5.16 + 6' 0.060
'I'icino 12.40 19.21 -35 0.23 17.78 8.61 +106 0.018
Brescia 5.38 9·85 I, 0.11 6.30 11.75 +33 0.33
Tufin 5.65 '.81 +16 0.13 6.29 3.21 + 93 0.063
Milan 3.96 ,.60 -29 0.1I1t 4.61 3.116 + 35 O.l~2
F1dem:a 3.43 6.01 -13 0.23 3.114 3.15 + 9 0.81
Gen01'll 3.96 3.91 + 1 0.98 2.16 3.00 - 6 0.84
Oars with low northerly winds
19 seeded, 25 not seeded 112 seeded, 37 not seeded
'ZUrich 11.32 6.90 -31 0·29 ,.)8 11.05 + 33 0.1.1
Neuchitel 3.55 11.19 -15 0.11 5."8 3.54 + 55 0.21
'I'icino 3.28 1.60 -32 0.42 11.03 8.16 + 26 0.56
Brescia 3.14 3.11 -15 0.62 6.22 3.12 + 61 0.11
Turin 2.98 3.21 - 9 0.86 5.02 9.18 -" 0.15
MHaa 1.95 2.46 -21 0.60 1.26 5.01 +" 0.31
Fiden:r.a 1;.113 2.41 +19 0.11 1.92 5·11 • 55 0.23
Genova 3.60 2.60 +36 0·51 6.31 5.28 • 1. 0.66
J. Ne"..., (9)
Table 2 reproduced frolll (8) and Fig. 3 give thE' results of these :!:tuhad to be
split into two parts, o~e with the areas of interest belnp: approximately
downwind and the other wab tbeu area5 being upWind. Any further stratif-ication5
requirE'd the analysis to be lIlade on a relatively small numbE:r or
observations, wi th the consequent decreal!!e In preci"ion. A so~ewhat lI:ore
in-depth lIIethodology, provides t.hE' pos5ibillty of studyin~ the wind direc­tion
influences usin@' all the available expnimental data simultaneously.
rhis lIlethodology, labeled "lIloving grid" or "mogrld" lIlethcdology, was
1eveloped (10) us1ng the idea of R.R. Braham who developed it fOT radar
lata.
The study of thE: AriZona uperillc.nt u"ing thE: lllOgr1ds (11) ends With
.he following ~ketch of a hypothE:tical lIIechani.:llll (P.H, for short) of the
J. Neyman (lZa)
3 HR. MOVING AvGS.
--SEEDED
------ NOT SEEDED
765
64 NS
S E WINOS
JO 15 20253035
HOUR
N W WINOS
025 295
f 8. 41 NS
~
020 0:
l!'
z .015 '" f\
0 z ! \v\
~ .010 § ~ \
0: "'i \
~ ,
0
,
Q.
JO is 20 25 30
tnJR
Fig. 4. Diurnal variation in hourly rainfall in Walnut Q.llch
when it was approximately downwind and when it was approximately
upwind from santa Catalina I>btmtains.
J. Neyman (13)
far-a1ol8Y lOiSsez ot rain:
·1he seecing 1118Y have initiated rain high above the Fround; ""hen
falling through dry a1r, this rain ev~porated and oecreased thE'
temperature; while carried downwind, the parcel of cool air evcn-tually
reached the ground and inhibited convection."
The relevance of the evaporation of rain before it reaches the l!l"ound
seell5 to bavl' been ftrst noticed in 1962 by LJ. korkman. 1 reyret
that I overlooked his publication for a 10nl: tll1le. Subsequent studios arc
due to Schiiepp, J. Joss and H.P. Roesli (12).
\Ie now proceed to assemble empirical evidence favoring the above
hn.,thetical mechanism. Indications are that this ll:ccr.anlSll opt'ralcd not
only during the Arizona experiment, but aho on tDe uninhibited updraft
day-, of Grossver:!'uch Ill. t:o~ver, some of the evidence indicates a
phenOlllenon not implied by the hi'l: large increases in rainfall cccurring in
certain conditions. The atmo~pheric-physlcal aspect of the.se conditions
appears as a very important problem.
J. A.S.
Figure 5, redrawn from a figure publl::lhed by/Slmpson and !Dennis (131,
illustrates the happenings to a SUIIllller cw:lulu.s cloUd SUbjected to :seediny'.
The legend states thtlt the figure represt!nts photoJl;raphs Ulustratiny thr
"cut-off tower rep-illle which often follows dynamic seedinp; of a dn;rle
cumulus." It/ah reference to tiM, Hg, 5 illustrates the fact that the rain
ln1tiated by seeding can e.stablbh a ·cut-off tOlOer rep:ilr.l',· pre:su:aably by
ccoling the lower part of the cloud. The tenD used by the two authors is
"precipitation break,· This, however, does not documEnt tinything tlbout the
Arizona experiment. Certain happenil\l~ at the Arizona cxperilllcnt are
lliustrated by fig. 6. This figure illu.strate.s the patterns of winds aloft
'ecorded by the 5 p.lI. raclio,sonde at Tuc!'on. Ihe:::e observations ellist for
J. Neyman (13a)
PANEL A: Cumulus at time of seeding.
PANEL B: Same cumulus 10 minutes after seeding.
PA~EL C: Same cloud, split into two parts.
18 minutes later.
Fig. 5. "Cut-off tmier regime which often fo11O\o1's dynamic
seeding of a single CUlIJlus."
J. Neyman (14)
210 experimental day~ of the Arizona experiment for wtlich the radiosonde
data are available. f'iS. 6 !tives an 1llu.!trative sample of the data. ~ach
vector of a seQuence give'" tht dirtction of the wind at a tpec1fied level
above the ground, llIeasured in 1II1l11bar~, frOlll 900 a:b. to 200 lIIb. Alse th"
length of the vector !tlve:! the lIind vf'loci ty. A closer inspt"ction of f ip.
6 ind icatcs two contra.sting type.s for ""hich the ~'Ork('rs at berkel£y Sta-tistieal
Laboratory invented th" descriptive terlls "pret:r;els" and "lont
fellows."
The term "pretzel" refers to thE: regia:fI' of practically no lIind:! aloft
that prevailed during the rdatively brief peried of the asc"nt of the
radiosonde. ObViously, on days lIith sclKling over the Santa CatnJinae
lIIarked by the pretnl winds occurring during the 2_t1 hours of seeding
operations, the "precipitation break" phf'nOl:lenon can be reflected only in
the target itself. en the other hand, on days \Oith "long fello~'" wina:! at
an ap~ropr1ate level occurring during seeding, the ·preci~itation break"
llu.!St be carrieo away. possibly to lIIanifest itself in solte other locality.
The importal'lt question is whether any such f"ffects arc reflecteo in
actual precipitation dat.a. Thf" relevant findings of Proff"5sor Batten arE'
published in twe papE>r.e1
4
)In his 1967 paper Battan ,hows that on days wit.h
seeding over the Santa Catalina Nountain.e, there were relatively !tore radar
echoes in the clol)(ls than on day.e without :seedint, and that. this diner­.
ence, indicating the initiation of rain, was concentrat~d on cloUO:: \;1th
top temperatures between -2t1°C and _30°C, very cold. 1t eeC1ll5 likel)' that.
these cloud.e had their bases high over the ground. In the oth£r paper,
publbhed a year earl1f'r, Eattan .etudied the prf"cipitation reaching the
ground in his target from' p.m. to 6 p.m., particularly with reference to
the indirectly ceasured height of the clOUd ba~e.
\' J Neyman (143) j'"mcow ~
570708 Dole' 570709
l 1
570729 570730
Y ~
PRETZEL
570820
580724
LONG
570821
580725
Fig. 6. A saJJt)le of wind patterns aloft at 5 p.lII. of experimental
days durilllt the Arizona Trilil.
J. Neyman (15)
Panels 1 and II of Table II give data taken frOlll Battan'S Tab~.!l 7 and
8 referring to Programs 1 and 2, rC.!lyectivdy. The three lines of cact:
table refEr to days with cloud basc.!! "low," "lIIedium," and "high" as
indirectly meai!!ured by the so-called "dew-point spread."
lhe six categories of experimental days ",.ith low, medlu:ll and hiF"h
cloUd bases during the two Programs of the experiment are unambiguous in
showing seed day deficiencies of rain in the target. Solnewhat contrary
the conclusion of Eattan, this fact could hardly be ascribed to chance. lr.
the absence of effects of seeding ar.d given strict randomization, the pro­bability
of the Observed results is (1/2)6 ~ 0.016, ",hich is a respectable
one tail significance probability.
Pand III of Table" represents a combination of i'anel:! 1 and II.
HerE: the estimated percent effect given in the last column is unambiguous:
the higher the cloud base, the larger the lo:u of rain ascribablE' to S('o-ing.
This result suegests that during Battan's seeding in the early aftcr-noons
the appropriate lev£! winds over the Santa Catalinas iIIust have been
In conSl.quence, the 5-hour precipitation alllounts, I p.m. to b p.Ill.,
on ....hich hattan's Tables 7 and 8 are based, reflect the full ,,;('iFllt 01 tl'.E'
"precipitation break" phenomenon recorded by ::'illp~on and Dcnnis.
This concludes the arguments suyportinl': the hypothetical mechanism of
(ar~a\;ay effects of local cloud seeding. This mechani:!Cll is bau(! on the'
• Simpson_Dennis phenOll!enon of -prt'cipitation break.- ...o ....e\·er, in addition
tc this phenomenon the h,.o authors mention anothcrf;;::ce:ctn~n;
labeled "orphan anvil".
-In both tropic~ and temperate latItude::: 'orphan anvils' frolll
I'latvral cumulo-nilllbus clouds arc foul'ld several hundred mile:!! and
lIIany hovre frOlll their ai te of origin. figur(' 29 .:lhc\o:s an
J. Ne)'1llan l ify the roogrid methodology in studying
the far-away effects in GTossversuch III (two panels on top) and in the
Arizona experiment (the lowest panel). There are 2 ranges of distances:
from 0 to about 140 kin. and from 140 kin. to about 280 kin. These are can-bined
with 4 ranges of the angle of winds: _45 0 to +450 from the day's wind
direction at a specified level ("downwind"), from 450 to 1350 ("to the right,"
etc.). In consequence, each panel of Fig. 7 provides room for evaluation
results in eight "cells". These cells are described as "far (or near)
downwind," as "far (or near) to the right," etc.
The lMgrids for Grossversuch III are based solely on raingage data from
the six shaded areas in Fig. I otber than ~1ilan. For this reason there are
no evaluation results for the four "near" cells.
The four numerical entires in particular cells are written in two lines.
Each top line gives mean rainfall on days with seeding and that on days without
seeding. The lower line &ives the estimated percent eff~ct, which can he
positive or negative. The second entry is the two-tail siWlificance probabi­lity.
Cases of significance are marked by underlining.
As an illustrative example, consider the top panel of Fig. 7. It corres­ponds
to Grossversuch III days with uninhibited updrafts, for which Table 2
exhibits a substantial prevalence of negative apparent effects of seedin(i:, both
with southerly and with northerly winds" none of them significant. Contrary to
this, the far-dowm,dnd cell sho\;'S a highly significant 61\ deficiency of seed d­rain
ascribable to seeding. How come? There are two reasons for this contrast
ll"le is that the evaluations in Table 2 are based on only 47 days with southerly
Ioinds and on 44 days with northerly winds, too few to achieve a substantial
power of the tests used. The other reason for the inconclusiveness of Table 2
may Io'ell be the crudeness of detenninin~ the degree of "dOW!l'l'.'indedness": the
Fig. 7
MOVING GRID RESULTS FOR
GRDSSVERSUCH III
AND fOR ARIZONA F.XPERIMEN1S
GROSSVERSUCH III
UNINH1BlT(O UPDRAFTS
GROSSVERSUCH III
STA81L1TY LAYERS
ARIZONA EXPERIMENTS
flRSTOAYS
J. Neyman (173)
./. Neyman (lSI
errors may have been in excess of 100°! Contrary to this, the mogrid methodo­logy
uses the towl 47 + 44 .. 91 days. Also, the error in deten'lining "down-windcdness,"
etc. had to be less than 45° either way. "ihile not too ~ressh
for sUTVeyors, this degree of precision appears encouraging for large scale
atJoospheric IOOtions.
The three panels of figure 7 exhibit indications of two intere~titlf
atmospheric phenotllena. One is the analoFY bch-een days ~ith uninhlbi~('O
updrafts at Grossversuch III and the Arizona experiment: in both cases the
far dOWl'llo'ind cdl is ~ar],ced by a larp:e and significant apparent 10i!S of
rain ascribable to ~eeding. Another 1nterestinp; detail 1s the pre~ence of
large and significant rainfall increases 11'1 the far cells to the right oj
the days' ..,ind direction for days with stability layers 11'1 Grossversuch III
and also for Ari2.ona.
The question is what could be th(' mechanism of these d1ffer('nccs in
rainfall on seeded and not seeded days? Thi~ question is of particular
where
1r::terest for Arizona I i111 otter evaluations indicated los::::cs or rain
ascribable to seeding. As is well ],cnolffl to meteorologists, there arc t\;O
distinct classes of SUDllDer convective clcuds: the "air lIless" and the
-frontaP eloeds. Could it be thet seeding of one of tr.('i!e categories
seeding of the other
decreases rain 11'1 the far down"'ind areas and that / increases rain in the
far areas to the right of the day's wind direction? And again: What is the
lI'IeChanism of this phenanenon?
J _ Neyman (19)
(i) "randomization has corne to be recognized as an essential part of
gathering trustworthy data about weather lOOdification", (li) "randomization ..
needed if we are to be able to use the resu1ts as solid evidence", (iii) 'The
details--not just slmllaries--need to be available... ". [Ref (2) of present
article.] While being in full agreement with all three statements, I feel that
statement (iii) requires illustrations.
Roughly, there are b.Q types of regrettable omissions. lXle is the anis-sion
of details of the experiments performed, of original data and of methodology
used for the evaluation. Not infrequently these details arc hard to get. A
somewhat different type of omission is illustrated by an article in the volume
Legal and SCientific Uncertainties of Weather Modification (Ed. W.A. Thanas,
Me University Press, 1977). The article in question is a",thored by L.J.
Battan. Its title is ''The Scientific Uncertainties: A Scientist Responds."
en p. 28 we read: "1 hasten to point out that data from a number of carefully
done c.oomercial seedings strongly suggest that the person who paid for the opera­tion
got a fair return on the investment." This remark, representing the opinion
of Professor Battan, is an interesting "detail". However, I miss another detail.
Ibis is that Professor Battan perfonned a cloud seeding experiment lasting seven
5l.D'11l"1ers, that his own evaluation for the first four-year long "Program" indicated
lO~ l,ess rain on days with seeding than on those without, and that his own
~altiation of the second "Program" of three smners also indicated a 30\ deficien­;
y of rain on days with seeding. !-Iy feeling is that this missing detail of
>rofessor Battan's S-page It •••A SCientist Fbspond·5" is rather relevant for a
;onference "en Legal and Scientific Uncertainties ... " Also, it seems important
:or the government and for the public at large.
Regretfully, a tendency to accept reports without insisting on "details"
.s reflected in Vol. I of Harlan Cleveland's Report to the U.S. Secretary of
:ootnerce. I't'hile one year of intense study may seem long, it is not sufficient
J. Neyman (1
for gathering all the important details and for their appraisal. As stated i"
my article (1). the fonnulation of a realistic national policy on weather rrod
fication requires the "Establishment of at least two philosophically differen
interdisciplinary research groltlS, inc1u:l.ing statisticians versed in experi­mental
~rk, perhaps members of the National Academy of Sciences, with a spec
mission to reevaluate the data of as many already perfonred cloud seeding expc
mcnts as possible, ~ continuation of properly planned experimentation.; The
suggested research groups should have unlimi ted access to the same data and hI
facilities for personal meetings to exchange ideas. They should be funded fn:
sources other than those engaged in funding cloud seeding." To be effective
this IIIJ1tigroup project should last not just one but at least three years. He:
fully, such a nultigroup project would examine the indications of the impressi
far~away effects of local cloud seeding, including the studies made in the
Berkeley Statistical Laboratory. Even with the greatest care blunders arc
difficult to avoid.
J. Neyll'lan (20)
REFERENCI:S AND NOTES
1. J. NeYllan, Proc. Nat. Acad. Sci. 74, 47H-4721 (1977).
2. H. Cleveland, (Chm.) Weather Modification Advisory Board,
The Manageraent of Weather Resources (U.S. Gov't Printing
Office, Washington, DC, 1978) Vols. I and II.
3. Grossversuch III ;tur Bekampfung des Hagel 1m Tessin. Seven
annual reports dated 1958·1964, available from Centrale Meteor-ologica
Svizzera, Osservatorio Ticinese, Locarno-Monti,
Swi tzerland.
4. L.J. Battan, J. App!. f>leteor. 5, 669-683 (1966); L.J. Sattan,
~6,317-322 (1967).
5. J. Neyman and II.B. Osborn, Proc. Nat. Acad. Sci. 68, 649-652
(1971) •
6. E.J. Smith, in Proc. Fifth Berkeley Symposium on Mathematical
Statistics and Probability, L. Lecalll and J. Neyman, Eds.
(University of California Press, Berkeley, 1967), 5, pp. 161­176;
P.A.P. Moran, Australian J. of Stat. I, 47-52 (1959).
7. J. Neyman, E.L. Scott and f>l.A. Wells, Proc. Nat. Acad. Sci.
60, 416-423 (1968); M. Neiburger and H.C. Chin, ~ 60,
424-431 (1968).
8. J. Neyman, et. aI, Rev. Intern. Stat. Inst. 37, 119-148
(1969) .
9. J. Neyman, et. aI, Proc. Nat. Acad. Sci. 69, 1348·1352
(1972) .
If). J. Neyman, et. aI, Proc. Nat. Acad. Sci. 68, 147-151 (1971);
R.R. Braham, Project Whitetop--Report to the National Science
Foundation (Dept. Geophys. Sci., Univ. Chicago, 1965).
J. Neyman l2l)
11. J. Neyman, et. aI, Proc. Nat. Acad. Sci. 10, 351~360
(1913) •
12. E.J. WorKman. Science 138. 401-412 (1962); M. Schuepp. J.
Joss and H.P. Roesli, J. Appl. Meteor. U. 183-781 (1964).
U. J. Simpson and A.S. Dennis, NOAA Technical Memorandum, ERL
OD-14 (Dept. of Commerce, Boulder, CO. 1912). pp. 1-148.
14. I thank Shyrl Dawkins. Kathie Hall, I>larilyn Hill, Jeanne.
Lovasich and M. Tere Sanabria for their concerted effort in
assembling the widely dispersed evidence and for the
general spirit of cooperation. This article was prepared
with partial support of the Office of Naval Research
(ONR N000147SC0159) and of the U.S. Army Research Office
(DA AG 2916G0161). This support is gratefUlly acknowledged.
All the opinions expressed in this article are those of the
author.